Scatter gather mediator improvements

[GDLMadushanka]

Current Limitation

Currently we can configure a min-messages value which is greater than max-messages. This does not give an error in either VSCode or runtime.
If min > max it seems the presedence is given to max check.

Also, we can give a min-messages number which is higher than the no of sequences. (This does not break the functionality, since if all the message flows get completed, it completes the aggregation)

Suggested Improvement

Add validation in VSCode and runtime

Version

4.4.0